Ad libitum caffeine consumption, cognitive performance, and sleep in special forces soldiers during a 96-h combat exercise.

Introduction: This observational study investigated the effects of sleep deprivation and ad libitum caffeine consumption on cognitive performance, risk behavior, and mood among 28 Israeli Special Forces (SF) soldiers (mean age: 20.57 ± 0.92 years) during a 96-hour combat exercise. Methods: Actigraphy was used to monitor sleep and activity; cognitive function, risk-taking propensity, mood states, and self-reported sleepiness were assessed using the Psychomotor Vigilance Task (PVT), Evaluation of Risks Scale (EVAR), Profile of Mood States (POMS), Karolinska Sleepiness Scale (KSS); and caffeine consumption by questionnaire at 0, 50, and 96 hours. For analyses, participants were divided into Low (<400 mg) and High (≥400 mg) caffeine consumption groups. Results: The soldiers hiked 108.5 ± 0.52 km and slept for 12.7 ± 0.5 h, with a notable transition from multiple short sleep epochs in the initial 50 hours to a consolidated 5-hour sleep period subsequently. In the High caffeine group, PVT reaction time was faster (p = 0.024) compared to the Low caffeine group, with fewer premature response errors (p = 0.026). However, this group showed increased risk-taking (p = 0.037), particularly reduced Self-Control (p = 0.010). No significant impact of ad libitum caffeine intake on mood was observed. However, degradation over the course of the exercise in both groups in mood states, including anger, fatigue, tension, and vigor, was noted (p < 0.05). KSS scores increased significantly at 50 and 96 h (p < 0.001). Discussion: These results suggest that while caffeine enhances cognitive function, its ad libitum consumption did not consistently improve these measures in this cohort of SF soldiers. The study highlights the complex relationship between sleep deprivation and caffeine intake and their combined effects on soldiers' cognitive and behavioral functions, indicating a need for evidence-based caffeine use guidelines for using caffeine in military settings.

Facial electromyography during exercise using soft electrode array: A feasibility study.

The use of wearable sensors for real-time monitoring of exercise-related measures has been extensively studied in recent years (e.g., performance enhancement, optimizing athlete's training, and preventing injuries). Surface electromyography (sEMG), which measures muscle activity, is a widely researched technology in exercise monitoring. However, due to their cumbersome nature, traditional sEMG electrodes are limited. In particular, facial EMG (fEMG) studies in physical training have been limited, with some scarce evidence suggesting that fEMG may be used to monitor exercise-related measurements. Altogether, sEMG recordings from facial muscles in the context of exercise have been examined relatively inadequately. In this feasibility study, we assessed the ability of a new wearable sEMG technology to measure facial muscle activity during exercise. Six young, healthy, and recreationally active participants (5 females), performed an incremental cycling exercise test until exhaustion, while facial sEMG and vastus lateralis (VL) EMG were measured. Facial sEMG signals from both natural expressions and voluntary smiles were successfully recorded. Stable recordings and high-resolution facial muscle activity mapping were achieved during different exercise intensities until exhaustion. Strong correlations were found between VL and multiple facial muscles' activity during voluntary smiles during exercise, with statistically significant coefficients ranging from 0.80 to 0.95 (p<0.05). This study demonstrates the feasibility of monitoring facial muscle activity during exercise, with potential implications for sports medicine and exercise physiology, particularly in monitoring exercise intensity and fatigue.

Practicing Emergency Medicine in the Metaverse: A Novel Mixed Reality Casualty Care Training Platform.

BACKGROUND: Current casualty care training modalities present several challenges, including limited simulation facilities, instructor dependence, lack of standardization, documentation of trainees' performance and training personalization. The study presents the design, development and preliminary evaluation of a novel hybrid training platform to address these challenges. METHODS: A mixed reality platform was chosen and developed to address field operators' requirements. The platform is easy to operate and can be set up by laypeople within 20-min in multiple environments. Individual-level training documentation is generated autonomously following each session, evaluating 30 aspects of performance. From this, a unique aggregated dataset emerges as a substrate for executives' dashboards and intelligent planning of future sessions. RESULTS: An evaluation process took part using simulator-based training in different stages along the project using a questionnaire (Likert-scale based). Fifty military physicians took part in an identical head injury scenario requiring airway management by endotracheal intubation and were immediately surveyed. CONCLUSION: TrauMR is an agile hybrid training that harbors the potential to address many of the emerging challenges of training for prehospital care in combat and civilian environments.

Heat Intolerance, Body Size, and Return to Duty.

BACKGROUND: Exertional heatstroke affects athletes and soldiers and can lead to temporary heat intolerance. The heat tolerance test (HTT) was developed to assist in the return-to-duty decisions of military personnel. Although there are several possible causes for heat intolerance, a soldier who fails the test is prevented from returning to serve in a front-line combat unit, regardless of the underlying reason.CASE REPORT: A 19-yr-old special infantry male soldier with unremarkable medical history collapsed during an afternoon hand-to-hand combat training session in the gym. The medic on site promptly initiated inefficient tap water cooling and measured a rectal temperature of 38.7 °C; he returned to duty the same evening. A few weeks later, after intensive physical training, he experienced exhaustion during a stretcher-carrying foot march. He was referred by the unit's physician, who suspected a condition of heat intolerance, to an HTT. The soldier underwent two HTTs, which were found to be positive. Consequently, he was discharged from serving in his infantry unit. No congenital or functional underlying causes could explain the diagnosis of heat intolerance.DISCUSSION: We discuss the possibility that the only explaining cause for the two positive HTTs was the soldier's anthropometric measures, particularly the low body surface area to body weight ratio. We raise the question of whether this soldier could have been returned safely to duty.Rabotin A, Epstein Y, Ketko I. Heat intolerance, body size, and return to duty. Aerosp Med Hum Perform. 2023; 94(7):546-549.

Lessons from outbreaks of COVID-19 at Israeli military bases.

BACKGROUND: To mitigate the spread of coronavirus disease 2019 (COVID-19), national guidelines, in accordance with international health authorities, mandated 14 days of quarantine for every close contact of a confirmed COVID-19 patient. Although health benefits are obvious, consequences are profound, especially for organizations required to maintain operational preparedness. OBJECTIVES: To present the Israel Defense Force (IDF) experience with outbreaks regarding quarantined individuals. To weigh the consequences of quarantined individuals needed for workforce and operation. METHODS: All positive COVID-19 cases in the IDF, as measured by a positive rRT-PCR test result, between 29 February and 18 May 2020 were evaluated. Numbers of positive individuals, quarantined individuals, and confirmatory exams conducted were collected. We compared the events in four units with the largest outbreaks and assessed the impact of confirmed cases, tests conducted, and workforce loss due to quarantine. RESULTS: Of the 187 soldiers who tested positive for COVID-19, source of infection was traced to 140 soldiers (75%). Almost no medical treatment was delivered, and hospitalization was rare. We found a median of 15.2% (interquartile range 5.3-34) for decline in unit workforce due to quarantine measures. Maximum reduction reached 47% of the workforce in one unit. CONCLUSIONS: Despite a relatively small number of confirmed cases, units underwent a substantial change in mode of operation due to the toll of quarantined individuals. In certain populations and organizations, perhaps a more liberal application of isolation and contact tracing is suitable due to the heavy economic burden and consequences in term of operational readiness.

Data Empowerment of Decision-Makers in an Era of a Pandemic: Intersection of "Classic" and Artificial Intelligence in the Service of Medicine.

BACKGROUND: The COVID-19 outbreak required prompt action by health authorities around the world in response to a novel threat. With enormous amounts of information originating in sources with uncertain degree of validation and accuracy, it is essential to provide executive-level decision-makers with the most actionable, pertinent, and updated data analysis to enable them to adapt their strategy swiftly and competently. OBJECTIVE: We report here the origination of a COVID-19 dedicated response in the Israel Defense Forces with the assembly of an operational Data Center for the Campaign against Coronavirus. METHODS: Spearheaded by directors with clinical, operational, and data analytics orientation, a multidisciplinary team utilized existing and newly developed platforms to collect and analyze large amounts of information on an individual level in the context of SARS-CoV-2 contraction and infection. RESULTS: Nearly 300,000 responses to daily questionnaires were recorded and were merged with other data sets to form a unified data lake. By using basic as well as advanced analytic tools ranging from simple aggregation and display of trends to data science application, we provided commanders and clinicians with access to trusted, accurate, and personalized information and tools that were designed to foster operational changes and mitigate the propagation of the pandemic. The developed tools aided in the in the identification of high-risk individuals for severe disease and resulted in a 30% decline in their attendance to their units. Moreover, the queue for laboratory examination for COVID-19 was optimized using a predictive model and resulted in a high true-positive rate of 20%, which is more than twice as high as the baseline rate (2.28%, 95% CI 1.63%-3.19%). CONCLUSIONS: In times of ambiguity and uncertainty, along with an unprecedented flux of information, health organizations may find multidisciplinary teams working to provide intelligence from diverse and rich data a key factor in providing executives relevant and actionable support for decision-making.

Short Communication: Combining Ethics With Efficiency-Israel Defense Forces' Experience in Clinical Trials During the Coronavirus Disease 2019 Pandemic.

The coronavirus disease 2019 (COVID-19) pandemic, first reported in China, soon spread worldwide, has evolved into one of the most complex global public health crises the world has encountered in the last several decades. Conducting military medical research is vital to study the unique influences of military service conditions on soldiers' health and to improve the medical response in various emergency periods. The Israel Defense Forces (IDF) Medical Corps maintains an Institutional Review Board (IRB) which reviews clinical studies conducted within the IDF. During the COVID-19 pandemic, the IRB of the IDF had to rapidly implement procedural modifications in order to comply with expanding urgent demands for research without compromising ethical standards. The ethical dilemmas and the IDF policy and perspective are outlined in this article.

Assessing rectal temperature with a novel non-invasive sensor.

Athletes, soldiers, and workers who perform intense physical activities under extreme hot conditions might encounter increased physiological thermal strain. Consequently, the increase in body core temperature (Tc) might result in heat exhaustion and heatstroke. Thus, continuously following changes in Tc is of utmost importance. Recently, the Tcore sensor (Dräger, Germany), which employs a unique dual-sensor heat flux technology, became commercially available to measure Tc, in a hospital-controlled environment. This study aimed to evaluate the possibility of using the Tcore sensor to accurately monitor rectal temperature (Tre), reflecting Tc, under exercise-heat stress. Thirteen healthy young males completed the study protocol, consisting of 90 min of moderate exercise (walking on a treadmill - 5 km/h, 4% elevation) under controlled hot/dry and hot/wet climatic conditions (30 °C/60% rh, 34 °C/40% rh, and 40 °C/40% rh). Tcore sensors were placed on the forehead and the left wrist. Temperatures from both Tcore sensors were recorded continuously together with Tre using a rectal thermistor. The original algorithm used by the company to estimate Tre from the Tcore sensor was found to be inadequate under the study's conditions and new models for the forehead and the wrist measurements were developed. Nearly 150,000 measurement sets (after filtering) were used to build independent MATLAB software algorithms and test their reliability according to the cross-validation algorithm. Bland-Altman analysis was used to compare between the results obtained by the new models to Tre. The database consisted of a large Tre range (36.5-38.9 °C). The mean errors of the models were close to zero, and the mean absolute errors were 0.20 ± 0.16 °C and 0.27 ± 0.20 °C for the forehead and wrist, respectively. 95% of the measurements from the forehead model and 86% from the wrist model were within ±0.5 °C of Tre, and 78% (forehead) and 64% (wrist) were within ±0.3 °C. Root Mean Square Deviation (RMSD) values were 0.29 °C and 0.40 °C for the forehead and wrist models, respectively. The developed models show the feasibility to use the Tcore sensor for assessing Tre under exercise-heat conditions. Furthermore, the sensor was found to be adequate for use on the wrist as well, which might be more practical for use in field conditions.

Self-reported symptoms in healthy young adults to predict potential coronavirus disease 2019.

OBJECTIVE: To assess the utility of self-reported symptoms in identifying positive coronavirus disease 2019 (COVID-19) cases among predominantly healthy young adults in a military setting. METHODS: A questionnaire regarding COVID-19 symptoms and exposure history was administered to all individuals contacting the Israeli Defence Forces Corona call-centre, before PCR testing. Surveyed symptoms included cough, fever, sore throat, rhinorrhoea, loss of taste or smell, chest pain and gastrointestinal symptoms. Factors were compared between positive and negative cases based on confirmatory test results, and positive likelihood ratios (LR) were calculated. Results were stratified by sex, body mass index, previous medical history and dates of questioning, and a multivariable analysis for association with positive test was conducted. RESULTS: Of 24 362 respondents, 59.1% were men with a median age of 20.5 years (interquartile range 19.6-22.4 years). Significant positive LRs were associated with loss of taste or smell (LR 3.38, 95% CI 3.01-3.79), suspected exposure (LR 1.33, 95% CI 1.28-1.39) and fever (LR 1.26, 95% CI 1.17-1.36). Those factors were also associated with positive PCR result in a multivariable analysis (OR 3.51, 95% CI 3.04-4.06; OR 1.86, 95% CI 1.65-2.09; and OR 1.34, 95% CI 1.19-1.51, respectively). Reports of loss of taste or smell increased gradually over time and were significantly more frequent during the late period of the study (63/5231, 1.21%; 156/7941, 1.96%; and 1505/11 190, 13.45%: p < 0.001). CONCLUSION: Loss of taste or smell, report of a suspicious exposure and fever (>37.5°C) were consistently associated with positive LRs for a positive SARS-CoV-2 PCR test result, in a population of predominantly young and healthy adults.

Mild Physical Activity Does Not Improve Spatial Learning in a Virtual Environment.

It is well-established that physical exercise in humans improves cognitive functions, such as executive functions, pattern separation, and working memory. It is yet unknown, however, whether spatial learning, long known to be affected by exercise in rodents, is also affected in humans. In order to address this question, we recruited 20 healthy young male adults (18-30 years old) divided into exercise and control groups (n = 10 in each group). The exercise group performed three sessions per week of mild-intensity aerobic exercise for 12 weeks, while the control group was instructed not to engage in any physical activity. Both groups performed maximal oxygen uptake (VO2max) tests to assess their cardiovascular fitness at baseline and every 4 weeks through the 12 weeks of the training program. The effects of mild aerobic exercise were tested on performance in two different virtual reality (VR)-based spatial learning tasks: (1) virtual Morris water maze (VMWM) and (2) virtual Radial arm water maze (VRAWM). Subjects were tested in both tasks at baseline prior to the training program and at the end of 12 weeks training program. While the mild-intensity aerobic exercise did not affect subjects' VO2max parameters, mean time to anaerobic threshold increased for the exercise group compared with control. No effect was observed, however, on performance in the VMWM or VRAWM between the two groups. Based on these results, we suggest that mild-intensity aerobic exercise does not improve spatial learning and memory in young, healthy adults.

[PHYSIOLOGICAL GENDER DIFFERENCES AND THEIR EFFECT ON COVID-19 CAUSED MORBIDITY].

INTRODUCTION: The coronavirus disease 2019 (COVID-19) outbreak has resulted in considerable morbidity and mortality, and caused comprehensive social and financial damages. Anatomical, physiological and occupational differences observed between men and women might influence the reaction to treatment and medications. This article reviews sex differences and their potential effect on COVID-19 infection, pathogenesis and prognosis in women compared to men.

Physiological Differences Between Heat Tolerant and Heat Intolerant Young Healthy Women.

Purpose: Heat intolerance (HI) is determined in the Israel Defense Force according to a heat tolerance test (HTT) before returning to duty after an exertional heat stroke (EHS) event. Recently, increased numbers of female combatants resulted in an increased number of EHS cases among women and a higher percentage of heat intolerance (HI) individuals. We aimed to evaluate the differences between tolerance to heat among women performing an HTT in relation to their menstrual cycle phase. Method: Thirty-three female participants were sorted into two groups: HI and heat tolerant (HT) according to two HTTs performed during both the luteal and follicular phases of the menstrual cycle or while consuming and during a break from consuming contraceptives. Results: HT women had an 18% higher maximal oxygen uptake (p < .005, 95% CI [2.6,9.8]) and 1.2% lower skin temperature in the HTT at the during and follicular phases (p < .01, 95% CI [0.12,0.77]) and 1.7% lower at the off and luteal phases (p < .001, 95% CI [0.34,0.92]). The mean sweat rate was 14% lower among the HI group only at the HTT at the during and follicular phases (p < .05, 95% CI (3,88)]). Conclusion: We found that HT can be predicted using aerobic capacity and core body temperature. Moreover, during the luteal phase, women presented altered thermoregulation that decreased the probability of being HT. This emphasizes the importance of considering the HT/HI criteria in the HTT for women, according to their aerobic ability and menstrual-cycle phase.

The relation between central variables, electromyography signals and peripheral microcirculation during intensive treadmill exercise.

BACKGROUND: Aerobic exercise under muscle fatigue can lead to muscular damage and injuries. Finding the correlations between central and peripheral microcirculation variables, as well as with electromyography signals of leg muscles during aerobic exercise, may contribute to early muscle fatigue identification. The goal of this study was to characterize the peripheral compensation following intensive exercise for assessment of muscle performance based on non-invasive techniques. METHODS: The experimental protocol included two days of measurements. Electrocardiography tests and anthropometric measurements of the volunteers (N = 14) were carried out. The maximal aerobic ability (first day), as well as electromyography and cutaneous hemodynamic variables (second day) were measured during treadmill run. A score-based Bayesian network machine-learning algorithm was used to predict ventilation values based on cutaneous hemodynamic measurements. FINDINGS: Transcutaneous oxygen tension can be used to identify anaerobic threshold for both trained and untrained subjects during treadmill running, while electromyography can be used to identify anaerobic threshold only of trained subjects. Predicted values of ventilation, based on the transcutaneous oxygen tension, showed high correlation with actual values. Prediction accuracy was better among trained subjects, compared to the untrained ones. INTERPRETATION: Transcutaneous oxygen tension could be used for prediction of maximal oxygen consumption during intense exercise and thus may provide improved assessment of premature fatigue during exercise.

Probability of Heat Intolerance: Standardized Interpretation of Heat-Tolerance Testing Results Versus Specialist Judgment.

CONTEXT: The heat-tolerance test (HTT) is a screening tool for secondary prevention of exertional heat illness by the Israel Defense Forces. To discern participant tolerance, recruits are exposed to intermediate environmental and exercise stresses, and their physiological responses, core temperature, and heart rate are monitored. When their physiological measures rise at a higher rate or exceed the upper levels of absolute values compared with other participants, heat intolerance (HI) is diagnosed. OBJECTIVE: To develop a mathematical model to interpret HTT results and provide a quantitative estimate of the probability of heat tolerance (PHT). DESIGN: Cross-sectional study. SETTING: Warrior Health Research Institute. PATIENTS OR OTHER PARTICIPANTS: The HTT results of 175 random individuals tested after an episode of exertional heat illness were classified qualitatively and then divided into training (n = 112) and testing (n = 63) datasets. All individuals were male soldiers (age range = 18-22 years) who had sustained an episode of definitive or suspected exertional heat stroke. MAIN OUTCOME MEASURE(S): Based on the decision algorithm used by the Israel Defense Forces for manual interpretation of the HTT, we designed a logistic regression model to predict the heat-tolerance state. The model used a time series of physiological measures (core temperature and heart rate) of individuals to predict the manually assigned diagnosis of HT or HI. It was initially fitted and then tested on 2 separate, random datasets. The model produced a single value, the PHT, and its predictive ability was demonstrated by prediction-density plots, receiver operating characteristic curve, contingency tables, and conventional screening test evaluation measures. RESULTS: According to prediction-density plots of the testing set, all HT patients had a PHT of 0.7 to 1. The receiver operating characteristic curve plot showed that PHT was an excellent predictor of the manual HT interpretations (area under the curve = 0.973). Using a cutoff probability of 0.5 for the diagnosis of HI, we found that PHT had sensitivity, specificity, and accuracy of 100%, 90%, and 92.06%, respectively. CONCLUSIONS: The PHT has the potential to be substituted for manual interpretation of the HTT and to serve in a variety of clinical and research applications.

Individualized estimation of human core body temperature using noninvasive measurements.

A rising core body temperature (Tc) during strenuous physical activity is a leading indicator of heat-injury risk. Hence, a system that can estimate Tc in real time and provide early warning of an impending temperature rise may enable proactive interventions to reduce the risk of heat injuries. However, real-time field assessment of Tc requires impractical invasive technologies. To address this problem, we developed a mathematical model that describes the relationships between Tc and noninvasive measurements of an individual's physical activity, heart rate, and skin temperature, and two environmental variables (ambient temperature and relative humidity). A Kalman filter adapts the model parameters to each individual and provides real-time personalized Tc estimates. Using data from three distinct studies, comprising 166 subjects who performed treadmill and cycle ergometer tasks under different experimental conditions, we assessed model performance via the root mean squared error (RMSE). The individualized model yielded an overall average RMSE of 0.33 (SD = 0.18)°C, allowing us to reach the same conclusions in each study as those obtained using the Tc measurements. Furthermore, for 22 unique subjects whose Tc exceeded 38.5°C, a potential lower Tc limit of clinical relevance, the average RMSE decreased to 0.25 (SD = 0.20)°C. Importantly, these results remained robust in the presence of simulated real-world operational conditions, yielding no more than 16% worse RMSEs when measurements were missing (40%) or laden with added noise. Hence, the individualized model provides a practical means to develop an early warning system for reducing heat-injury risk. NEW & NOTEWORTHY A model that uses an individual's noninvasive measurements and environmental variables can continually "learn" the individual's heat-stress response by automatically adapting the model parameters on the fly to provide real-time individualized core body temperature estimates. This individualized model can replace impractical invasive sensors, serving as a practical and effective surrogate for core temperature monitoring.

The validity of the heat tolerance test in prediction of recurrent exertional heat illness events.

OBJECTIVES: Heat-tolerance-testing (HTT) protocol is used as a screening test for secondary prevention of exertional heat illness (EHI) in the military. Subjects whose test results are positive (heat-intolerant, HI) are presumed to be at higher risk of repeated EHI events than heat-tolerant subjects (HT) and are therefore prevented from return to combat duty, but may return to unsupervised recreational activity. Our aim was to determine, whether HTT results predict the risk of repeated episodes of exertional heat illness (EHI). DESIGN: Retrospective cohort. METHODS: One-hundred-forty-five subjects (110 HT, 35 HI) who were diagnosed with an EHI event by a physician and underwent HTT during 2008-2015 were contacted and asked about recurrence of EHI. Incidence of recurrent events was reported as number of cases per 1000 person-years. Ratio of events among HI and HT individuals was presented as rate ratio (RR) and its 95% confidence interval. RESULTS: Of the 145 patients, six (4.1%) had experienced recurrent EHI events (10.63 per 1000PY): four HI subjects (11.4%, 26.6 per 1000PY) and two HT (1.8%, 4.8 per 1000PY) (RR=5.504, CI 95%=1.01-30, p=0.027). Only one of the six recurrent events was a heat stroke (HT individual), other five were heat exhaustions. Sensitivity, specificity and diagnostic accuracy of HTT were 66.7%, 77.7% and 77.2%, respectively. CONCLUSIONS: The risk of EHI recurrence is measurable and can be discussed with patients before they return to sports. A referral to HTT can be considered, as negative HTT result is associated with substantial and significant EHI risk reduction.

Measuring core body temperature with a non-invasive sensor.

In various occupations, workers may be exposed to extreme environmental conditions and physical activities. Under these conditions the ability to follow the workers' body temperature may protect them from overheating that may lead to heat related injuries. The "Dräger" Double Sensor (DS) is a novel device for assessing body-core temperature (Tc). The purpose of this study was to evaluate the accuracy of the DS in measuring Tc under heat stress. Seventeen male participants performed a three stage protocol: 30min rest in a thermal comfort environment (20-22°C, 50% relative humidity), followed by an exposure to a hot environment of 40°C, 40% relative humidity -30min at rest and 60min of exercise (walking on a treadmill at 5km/h and 2% elevation). Simultaneously temperatures measured by the DS (TDS) and by rectal temperature (Tre) (YSI-401 thermistor) were recorded and then compared. During the three stages of the study the average temperature obtained by the DS was within±0.3°C of rectal measurement. The correlation between TDS and Tre was significantly better during the heat exposures phases than during resting under comfort conditions. These preliminary results are promising for potential use of the DS by workers under field conditions and especially under environmental heat stress or when dressed in protective garments. For this goal, further investigations are required to validate the accuracy of the DS under various levels of heat stress, clothing and working levels.

Wheeled assistive device for load carriage - the effects on human gait and biomechanics.

Soldiers are often required to carry loads which impose biomechanical strain on the human body. This can adversely affect physical performances. Recently, wheel-based devices (WBD) were designed to reduce the load on the soldier. In the present study, a prototype of this newly developed WBD was evaluated. Thirteen volunteers performed three exercise protocols on a treadmill as follows: (1) no load; (2) carrying 40% of their bodyweight with a backpack or; (3) with the WBD. Data acquisition included: gait parameters, vertical ground reaction forces (VGRF) and contact pressure acting on the shoulder. Biomechanical analysis showed that the WBD decreased the contact pressure on the shoulder and the VGRF. However, greater gait variability, in terms of cycle-to-cycle gait line generation, was observed, which might point to a difficulty in maintaining stability while walking. The study suggests that WBD has a potential to reduce the biomechanical strain on the soldier while carrying heavy loads. Future potential adjustments for the development of a better WBD-based solution are suggested. Practitioner Summary: The present research observed the potential biomechanical advantages of using a wheel-based device designed to reduce the load on the soldier. It contributed to a lower mechanical force on the soldier's body, yet causing modulations in gait control. Future design adjustments should be made to optimise the platform.

The effects of smoking and nicotine ingestion on exercise heat tolerance.

BACKGROUND: Smoking has a thermogenic effect and is associated with low physical performance. Nevertheless, a direct, quantitative effect of acute smoking on exercise heat tolerance has not been reported. METHODS: Sixteen healthy young male volunteers, eight cigarette smokers, and eight non-smokers participated in the study. All subjects performed a maximal oxygen consumption test (VO2max) and a standardized heat tolerance test (HTT) after at least 12 h without smoking under the following conditions: no nicotine exposure, 10 min after nicotine exposure (2 mg nicotine lozenge), and 10 min after smoking two cigarettes (0.8 mg nicotine in each cigarette, smokers only). RESULTS: There was no significant effect of nicotine exposure on physiological performance and heat tolerance in the non-smokers group. In the smokers group, cigarette smoking, but not nicotine ingestion, resulted with higher heart rate (by 9±9 bpm) at the end of the HTT (p<0.05). Moreover, both smoking and nicotine ingestion increased smokers' rectal temperature at the end of the HTT (by 0.24±0.16°C and 0.21±0.26°C, respectively, p<0.05) and were associated with higher sweat rate during the HTT (by 0.08±0.07 g/h and 0.06±0.08 g/h, respectively, p<0.05). Heart rate variability (HRV) analysis also revealed a higher LF/HF (low frequency/high frequency) ratio after exposure to nicotine and smoking in the smokers group compared with no exposure (2.13±2.57 and 2.48±2.76, respectively, p<0.05), indicating a higher sympathetic tone. CONCLUSIONS: According to this preliminary study, cigarette smoking and nicotine ingestion increase the physiological strain during a HTT in smokers. Acute smoking may, therefore, increase heat intolerance and the risk to heat injuries.

Physiological Evaluation of a Wheeled Assistive Device for Load Carriage.

Carrying heavy weight imposes high physiological strain on the human body, which can adversely affect physical performance. This is especially important for soldiers whose physical performance level may influence mission completion and survival. Recently, wheel-based devices (WBDs), designed to reduce the load on the soldier, have been suggested as a possible solution. Thus, the aim of this study was to evaluate the physiological effects of a proposed WBD prototype. Ten volunteers performed 3 exercise protocols on a treadmill as follows: without carrying any load, with a military backpack, and with the WBD. While using both modalities, they carried 40% of their body weight. Data acquisition included heart rate, body core temperature, oxygen consumption, and subjective comfort. Postural sway was also measured to evaluate the effect of WBD on standing balance. There were no significant differences between the physiological measures while using both modalities. Subjective comfort evaluation showed that the WBD may be more comfortable, yet it raises difficulty in maintaining balance while walking, as can be explained by the postural sway results. We suggest that the similarity in physiological strain while using the WBD was due to reduced walking efficiency in an attempt to maintain balance. It appears that the WBD may have some biomechanical advantages in reducing the subjective pain and pressure at the shoulder region, a matter that should be further examined together with other biomechanical measures.